The Collaborative International Dictionary of English v.0.48:

Attentive \At*ten"tive\ ([a^]t*t[e^]n"t[i^]v), a. [Cf. F.
   attentif.]
   1. Heedful; intent; observant; regarding with care or
      attention.
      [1913 Webster]

   Note: Attentive is applied to the senses of hearing and
         seeing, as, an attentive ear or eye; to the application
         of the mind, as in contemplation; or to the application
         of the mind, in every possible sense, as when a person
         is attentive to the words, and to the manner and
         matter, of a speaker at the same time.
         [1913 Webster]

   2. Heedful of the comfort of others; courteous.
      [1913 Webster]

   Syn: Heedful; intent; observant; mindful; regardful;
        circumspect; watchful.
        [1913 Webster] -- At*ten"tive*ly, adv. --
        At*ten"tive*ness, n.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

attentiveness \at*ten"tive*ness\ n.
   1. the quality of paying careful attention; attentiveness to
      detail.

   Syn: heed, regard, paying attention.
        [PJC]

   2. paying particular notice (as to children or helpless
      people).

   Syn: heed, regard, paying attention.
        [WordNet 1.5]

   3. the trait of being considerate and thoughtful of others.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

attentiveness
    n 1: paying particular notice (as to children or helpless
         people); "his attentiveness to her wishes"; "he spends
         without heed to the consequences" [syn: attentiveness,
         heed, regard, paying attention] [ant: heedlessness,
         inattentiveness]
    2: the trait of being considerate and thoughtful of others
    3: the trait of being observant and paying attention [ant:
       inattentiveness]